$re = '/^([a-z]+\.?[a-z]?)*[a-z]+$/mi';
$str = 'hi.man
hi.man.hi.man
hiMan
hi, man.
hi, man 12
hi, man 1.2
hi man
hi,man
hd.dh.h
das..dsa
d.d.d
dd.ddd.d..d
d.d.dddas.';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php